Mark @llvm.trap cold

[vsk]

Summary

A call to @llvm.trap can be expected to be cold (i.e. unlikely to be
reached in a normal program execution).

Outlining paths which unconditionally trap is an important memory
saving. As the hot/cold splitting pass (imho) should not treat all
noreturn calls as cold, explicitly mark @llvm.trap cold so that it can
be outlined.

Split out of https://reviews.llvm.org/D54244.

llvm/trunk/docs/LangRef.rst

 '``llvm.trap``' Intrinsic
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Syntax:
 """""""
 
 ::
 
-      declare void @llvm.trap() noreturn nounwind
+      declare void @llvm.trap() cold noreturn nounwind
 
 Overview:
 """""""""
 
 The '``llvm.trap``' intrinsic.
 
 Arguments:
 """"""""""

llvm/trunk/include/llvm/IR/Intrinsics.td

 // ReadNone - The specified argument pointer is not dereferenced by the
 // intrinsic.
 class ReadNone<int argNo> : IntrinsicProperty {
   int ArgNo = argNo;
 }
 
 def IntrNoReturn : IntrinsicProperty;
 
+// IntrCold - Calls to this intrinsic are cold.
+// Parallels the cold attribute on LLVM IR functions.
+def IntrCold : IntrinsicProperty;
+
 // IntrNoduplicate - Calls to this intrinsic cannot be duplicated.
 // Parallels the noduplicate attribute on LLVM IR functions.
 def IntrNoDuplicate : IntrinsicProperty;
 
 // IntrConvergent - Calls to this intrinsic are convergent and may not be made
 // control-dependent on any additional values.
 // Parallels the convergent attribute on LLVM IR functions.
 def IntrConvergent : IntrinsicProperty;

 def int_coro_subfn_addr : Intrinsic<[llvm_ptr_ty], [llvm_ptr_ty, llvm_i8_ty],
                                     [IntrReadMem, IntrArgMemOnly, ReadOnly<0>,
                                      NoCapture<0>]>;
 
 ///===-------------------------- Other Intrinsics --------------------------===//
 //
 def int_flt_rounds : Intrinsic<[llvm_i32_ty]>,
                      GCCBuiltin<"__builtin_flt_rounds">;
-def int_trap : Intrinsic<[], [], [IntrNoReturn]>,
+def int_trap : Intrinsic<[], [], [IntrNoReturn, IntrCold]>,
                GCCBuiltin<"__builtin_trap">;
 def int_debugtrap : Intrinsic<[]>,
                     GCCBuiltin<"__builtin_debugtrap">;
 
 // Support for dynamic deoptimization (or de-specialization)
 def int_experimental_deoptimize : Intrinsic<[llvm_any_ty], [llvm_vararg_ty],
                                             [Throws]>;
 

llvm/trunk/test/Feature/intrinsics.ll

 declare void @llvm.trap()
 
 define void @trap() {
   call void @llvm.trap()
   ret void
 }
 
 ; CHECK: attributes #0 = { nounwind readnone speculatable }
-; CHECK: attributes #1 = { noreturn nounwind }
+; CHECK: attributes #1 = { cold noreturn nounwind }

llvm/trunk/test/Transforms/SimplifyCFG/switch-on-const-select.ll

bees:
     unreachable
 }
 
 declare void @llvm.trap() nounwind noreturn
 declare void @bees.a() nounwind
 declare void @bees.b() nounwind
 
 ; CHECK: attributes [[$NUW]] = { nounwind }
-; CHECK: attributes #1 = { noreturn nounwind }
+; CHECK: attributes #1 = { cold noreturn nounwind }

llvm/trunk/utils/TableGen/CodeGenIntrinsics.h

struct CodeGenIntrinsic {
   bool canThrow;
 
   /// True if the intrinsic is marked as noduplicate.
   bool isNoDuplicate;
 
   /// True if the intrinsic is no-return.
   bool isNoReturn;
 
+  /// True if the intrinsic is cold.
+  bool isCold;
+
   /// True if the intrinsic is marked as convergent.
   bool isConvergent;
 
   /// True if the intrinsic has side effects that aren't captured by any
   /// of the other flags.
   bool hasSideEffects;
 
   // True if the intrinsic is marked as speculatable.

llvm/trunk/utils/TableGen/CodeGenTarget.cpp

CodeGenIntrinsic::CodeGenIntrinsic(Record *R) {
   TheDef = R;
   std::string DefName = R->getName();
   ModRef = ReadWriteMem;
   Properties = 0;
   isOverloaded = false;
   isCommutative = false;
   canThrow = false;
   isNoReturn = false;
+  isCold = false;
   isNoDuplicate = false;
   isConvergent = false;
   isSpeculatable = false;
   hasSideEffects = false;
 
   if (DefName.size() <= 4 ||
       std::string(DefName.begin(), DefName.begin() + 4) != "int_")
     PrintFatalError("Intrinsic '" + DefName + "' does not start with 'int_'!");
for (unsigned i = 0, e = PropList->size(); i != e; ++i) {
     else if (Property->getName() == "Throws")
       canThrow = true;
     else if (Property->getName() == "IntrNoDuplicate")
       isNoDuplicate = true;
     else if (Property->getName() == "IntrConvergent")
       isConvergent = true;
     else if (Property->getName() == "IntrNoReturn")
       isNoReturn = true;
+    else if (Property->getName() == "IntrCold")
+      isCold = true;
     else if (Property->getName() == "IntrSpeculatable")
       isSpeculatable = true;
     else if (Property->getName() == "IntrHasSideEffects")
       hasSideEffects = true;
     else if (Property->isSubClassOf("NoCapture")) {
       unsigned ArgNo = Property->getValueAsInt("ArgNo");
       ArgumentAttributes.push_back(std::make_pair(ArgNo, NoCapture));
     } else if (Property->isSubClassOf("Returned")) {

llvm/trunk/utils/TableGen/IntrinsicEmitter.cpp

if (L->canThrow != R->canThrow)
       return R->canThrow;
 
     if (L->isNoDuplicate != R->isNoDuplicate)
       return R->isNoDuplicate;
 
     if (L->isNoReturn != R->isNoReturn)
       return R->isNoReturn;
 
+    if (L->isCold != R->isCold)
+      return R->isCold;
+
     if (L->isConvergent != R->isConvergent)
       return R->isConvergent;
 
     if (L->isSpeculatable != R->isSpeculatable)
       return R->isSpeculatable;
 
     if (L->hasSideEffects != R->hasSideEffects)
       return R->hasSideEffects;
if (ae) {
         OS << "};\n";
         OS << "      AS[" << numAttrs++ << "] = AttributeList::get(C, "
            << attrIdx << ", AttrParam" << attrIdx << ");\n";
       }
     }
 
     if (!intrinsic.canThrow ||
         intrinsic.ModRef != CodeGenIntrinsic::ReadWriteMem ||
-        intrinsic.isNoReturn || intrinsic.isNoDuplicate ||
+        intrinsic.isNoReturn || intrinsic.isCold || intrinsic.isNoDuplicate ||
         intrinsic.isConvergent || intrinsic.isSpeculatable) {
       OS << "      const Attribute::AttrKind Atts[] = {";
       bool addComma = false;
       if (!intrinsic.canThrow) {
         OS << "Attribute::NoUnwind";
         addComma = true;
       }
       if (intrinsic.isNoReturn) {
         if (addComma)
           OS << ",";
         OS << "Attribute::NoReturn";
         addComma = true;
       }
+      if (intrinsic.isCold) {
+        if (addComma)
+          OS << ",";
+        OS << "Attribute::Cold";
+        addComma = true;
+      }
       if (intrinsic.isNoDuplicate) {
         if (addComma)
           OS << ",";
         OS << "Attribute::NoDuplicate";
         addComma = true;
       }
       if (intrinsic.isConvergent) {
         if (addComma)